<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>字体粗细</title>
  <style>

    .words{
      font-weight: normal;
    }
    .number{
      font-weight: 400;
    }
    .cat{
      font-weight: bold;
    }
    .dog {
      font-weight: 700
    }
  </style>
</head>
<body>
  <p class="words">今天的天气真不错</p>
  <p class="number">天气一点点热</p>
  <p class="cat">我的小猫暴脾气</p>
  <p class="dog">我的小猫容易炸毛</p>
</body>
</html>